This section provides background information related to the present disclosure and is not necessarily prior art.
Nail-like fasteners have been used for thousands of years. Some archeological evidence suggests that nail-like fasteners may have been used in Mesopotamia as long ago as 3500 B.C. Early nails were forged or shaped with hammers. Several millennia later in the 1500s A.D. machines were developed to produce a “cut-nail” fastener from a strip of iron. Not until the mid-1800s were machines and methods developed to produce nail-like fasteners made from metal wire. Most nail-like fasteners of the present day are still produced by machines, methods, and techniques that utilize a metal wire forming process.
At the beginning of the American Revolution, England held the distinction of being the world's leading producer of nails. At that time, there was essentially no nail production taking place in the American Colonies on a commercial scale. As a result many Colonial households setup a simple nail manufacturing process in their homes using home fires as a manufacturing tool. Colonist made nails for their own use as well as for bartering for other goods and services. The first wide spread manufacture of wire nails in the USA was in 1877-1879 using iron wire from Norway. Wire nails had been used in Norway for many years prior to their introduction to the USA construction market. Testing as early as the year 1884, conducted by the Watertown Arsenal, in Watertown, Mass., revealed that cut-nails had superior withdrawal resistance compared to iron wire nails. However, because the wire nails could be produced at significantly lower cost than cut-nails, the construction industry gravitated to wire nails and away from cut-nails. Now, over 130 years later, there are over 2,000 varieties of nail-like fasteners being produced in modern times.
Nail-like fasteners are used for many purposes and are designed for use in many types of materials and/or applications. One application is in the wood frame construction industry, where nail-like fasteners are utilized to fasten wood and/or wood-like materials together. In general, the construction industry has many applications for residential and/or commercial structures using structural substrate components made of wood and/or wood-like materials. The wood and/or wood-like substrate materials receive fastener devices that are applied to restrain and/or couple the wood and/or wood-like substrate materials to one another and to other construction components. Typical fasteners such as nails, screws, and bolts generally include a longitudinally extending shank and a head that extends radially outwardly from the end of the shank.
Many standard nails are loose, which facilitate being driven by hand while many other nails are collated or coiled in some fashion to facilitate use with a powered delivery system. In a similar fashion, screws are available for application by hand and/or powered delivery systems. Typically, bolted fasteners are manually installed while final torque is either applied manually or with the assistance of a powered system. There are many features applied to the shanks of nails, screws, and bolts to assist the retention and holding strength of the fastener. Some features that have been applied to the shank of nail-like fasteners include special coatings, spiral twisting, ring shanks, knurls, barbs, ribs, and splines, just to name a few. Some nail-like and/or screw-like fasteners combine multiple shank features on the same shank. In similar fashion, screw-like and bolt-like shanks feature many different kinds of thread patterns, continuous threads, discontinuous threads, single flutes, multiple flutes, special coatings, and combinations of thread patterns on the same shank, just to name a few. Even though many variations exist, the heads of most fasteners used in residential and commercial construction to connect and/or restrain wood and/or wood like materials are relatively small in size. Furthermore, the heads of most typical fasteners are designed and manufactured in such a way that they cut and/or rupture surface fibers of the substrate material.
When a typical fastener is installed in a typical wood and/or wood-like substrate material, a tug-a-war of sorts results between the substrate material and the fastener. For instance, a typical plywood roof decking substrate material of a typical wood frame construction is fastened to a wood rafter framing substrate material using a nail. In many regions near coastal areas prone to high wind storms, building codes require at least an 8 d nail applied in a prescribed pattern and spacing in order to achieve a safe working load design. The tug-a-war in this scenario plays out during a high wind storm as the roof decking substrate material is challenged to come off and separate from the wood rafter framing substrate material. Effectively, the only thing holding the roof decking substrate material together with the wood rafter substrate material are the nails. The nail shanks are challenged to not withdraw from the wood rafter substrate material while at the same time the nail head is challenged to not pull-through the roof decking substrate material.
The weakest link in the pull-through withdrawal tug-of-war will fail first such that one of three failure modes results. In the first failure mode, the nail shank will withdraw from the wood rafter substrate material so that the nail head remains embedded in the roof decking substrate material (i.e. the roof decking substrate material lifts off the wood rafter substrate material taking the nails with it.) In the second failure mode, the nail head will pull-through the roof decking substrate material and the nail shank will remain embedded in the wood rafter substrate (i.e. the roof decking substrate material lifts off the wood rafter substrate material while the nails remain in the wood rafter substrate material). A third failure mode, less common than the first and second failure modes, is fastener failure, where the nail head or the shank fails due to breakage, bending, or shearing. When any one of these three failure modes occur, the wood roof decking substrate material comes off resulting in the building suffering extensive damage and property loss.
Independent third party lab testing conducted by NTA, Inc. has demonstrated that commonly used nails lose as much as half of their initial withdrawal resistance within two days of being driven in place. Then after about a month later, the wood fibers of the substrate material will cooperate with the nail to slightly increase its withdrawal resistance, though the final withdrawal resistance will still be significantly less than the initial resistance.
Shank features such as barbs, ring shanks, spirals, and flutes have been shown to lose significant withdrawal resistance when the substrate material is subjected to environmental conditions, which causes the dry shrinking of wood substrate fibers over long periods of time. In addition, shank features such as barbs, ring shanks, spirals, and flutes have been shown to lose significant withdrawal resistance when the nail and substrate material are subjected to vibration, which may be created by storm winds beating upon a structure, seismic activity generated by tornadoes beating the ground as they travel, and seismic activity associated with earth quakes and ground shifting.
Examples of nail-like fasteners include those disclosed in U.S. Pat. No. 387,380 entitled “Flat Pointed Nail or Tack,” which issued to J. F. Thayer on Aug. 7, 1888, U.S. Pat. No. 2,093,610 entitled “Nail,” which issued to S. Kraemer on Sep. 21, 1937, and U.S. Pat. No. 4,932,820 entitled “Nail With Differential Holding Capabilities Along Its Shank,” which issued to Schniedermeier on Jun. 12, 1990. One short coming of the fasteners described in these patents is that the heads can easily cut and/or rupture the surface fibers of the wood and/or wood-like substrate material. Another significant shortcoming of fasteners of this type is that the pull-through resistance of the fastener does not increase proportionally with an increase in the thickness of the substrate material. Independent third party testing by NTA, Inc. reveals that as the thickness of the substrate material increases, the pull-through resistance of such fasteners increases to a lesser extent.
Some people in the construction industry have improvised and resorted to using a flat washer under the head of the fastener to enlarge the effective bearing surface of the fastener. While using a washer-type device does increase the bearing surface, it also increases the relative thickness of the head of the fastener causing it to protrude above the surface of the substrate material. If the fastener and washer combination is driven in to be flush with the surface of the substrate material, then the substrate material can often be cut, compromised, and/or damaged such that it is easily susceptible to further deformation and subsequent loss of structural integrity.
Examples of nail-like fasteners used in combination with a washer-like device include U.S. Pat. No. 2,256,401 entitled “Fastener,” which issued to H. Maze on Sep. 16, 1941, U.S. Pat. No. 4,860,513 entitled “Roofing Fastener,” which issued to Whitman on Aug. 29, 1989, and U.S. Pat. No. 4,884,932 entitled “Decking Insulation Fastener,” which issued to Meyer on Dec. 5, 1989. A short coming of the fasteners disclosed in these patents includes that the washer-like devices are not designed to prevent cutting and/or rupturing the surface fibers of the wood and/or wood-like material substrate. Similar to the way a nail head ruptures the surface fibers of the wood substrate, the washer-like device does so as well, but at a larger diameter than the nail head diameter.
Others have developed nails with enlarged heads to increase the effective bearing surface of the fastener. For example, U.S. Pat. No. 6,758,018 entitled “Power Driven Nails For Sheathing Having Enlarged Diameter Heads For Enhanced Retention And Method,” which issued to Sutt, Jr. on Jul. 6, 2004, discloses a fastener with an enlarged head requiring a specific ratio between the size of the head and the size of the shank. The enlarged head specified by this ratio results in increased pull-through resistance compared to commonly used nails. Fasteners available in the marketplace under the brand name “Hurriquake” are a derivative of this patent. Testing reveals that fasteners of this type do exhibit increased pull-through resistance compared to fasteners having a smaller tradition sized head. However, when subjected to the destructive forces of only moderate wind storms the modest improvement in retention force that is realized with such fasteners is basically mute, still allowing pull-through, and still resulting in a loss of structural integrity. As a result, higher wind load forces associated with Category-5 hurricanes and/or EF-5 tornadic storm events easily overcome the benefits of such fasteners. One of the shortcomings of this design is that the geometric features of the nail head are relatively flat and planar. Therefore, the benefit of the enlarged head size compared to the shank of the fastener is limited because of the inherent detrimental benefits of the geometric shape of the head design. Specifically, enlarged head nails have been shown to include several significant failure modes. One failure mode occurs where the surface fibers of the wood substrate material become ruptured and split from the initial setting of the nail before pull-through forces are applied. Another failure mode occurs where the enlarged heads of the nails become noticeably distorted and wobbled after pulling through the substrate material, resembling an umbrella turned inside out as a result of strong winds. Yet another significant shortcoming observed in the testing was that the corresponding pull-through resistance of the nails tested in various thicknesses of substrates materials was not equivalent to the increased thickness of the substrate. In other words, in spite of the enlarged head, independent third party testing reveals that as the thickness of the substrate material increases, there is not a corresponding increase in the pull-through resistance for nails of this design.
Accordingly, there remains a need for an improved fastener head design that increases pull-through resistance of nail-like fasteners, screw-like fasteners, and bolt-like fasteners.